The present invention relates, in general, to ignition controllers and methods for use with internal combustion engines. More particularly, the speed dependent ignition controller and method of the present invention is of especial utility for providing an engine speed variable dwell control signal for terminating dwell and implementing retard and advance of ignition timing useful in the startup and sustained running of internal combustion engines.
During startup and at other times of generally low engine speed, it is of course desirable to retard the ignition of the air/fuel mixture in an internal combustion engine so as to avoid the kickback caused by ignition of the air/fuel mixture before the piston reaches top dead center. Conversely, at higher engine speeds, ignition is commenced before the piston reaches top dead center, which, due to the finite time span involved in fully igniting the mixture, will result in a desired power stroke after passage of the top dead center position.
In either instance, whether at a retard or advance ignition position, spark occurrence is initiated after a specific dwell time; dwell time being that finite length of time during which current is available to charge the ignition coil to fire the spark plug. At slow engine speeds this finite length of time required to charge the coil corresponds to a relatively small angular displacement of the engine crankshaft and therefore relates to a small dwell angle. At higher engine speeds on the other hand, a greater dwell angle corresponds to the same dwell time and therefore dwell initiation must occur earlier.
To this end, there have previously been disclosed numerous mechanical spark occurrence advance mechanisms for centrifugal or vacuum switching between a fixed retard and advance angle for use with simple engine ignition systems, and similar mechanical dwell control mechanisms were utilized. More recently, numerous electronic circuits have been proposed which have, to some extent, eliminated many of the problems and costs inherent in the earlier mechanical systems. However, these electronic systems have themselves been relatively complex, requiring numerous individual components or sensors and therefore themselves somewhat costly to produce and concomitantly prone to failure by virtue of the number of components involved.
It is therefore an object of the present invention to provide an improved speed dependent ignition controller and method.
It is further an object of the present invention to provide an improved speed dependent ignition controller and method which is readily and inexpensively implemented.
It is still further an object of the present invention to provide an improved speed dependent ignition controller and method which simplifies the establishment of spark retard for starting and spark advance for sustained run speeds.
It is still further an object of the present invention to provide an improved speed dependent ignition controller and method which provides selective utilization of a single engine sensor having as an output a signal having a pulse width proportional to the difference between a desired ignition advance and retard angle.